The Los Angeles County sheriff has escalated his war of words against California medical marijuana dispensaries, saying as many as 97 percent operate as criminal enterprises.

Some of the pot shops get marijuana from Mexican drug cartels, and most dole out pot to people with no medical need for it, Sheriff Lee Baca said.

"Millions of dollars are being made for profit, and it's all illegal," the sheriff said this week.

Baca presented no evidence to support his claim. His comments coincided with a recent announcement that he would lead efforts against a November ballot measure to legalize marijuana for personal use in California.

Critics said his claims about the dispensaries were politically motivated and untrue.

"When they run out of scare tactics, they come out with stuff like this," said Michael Backes, a board member of the Cornerstone Research Collective, which provides marijuana to patients in the Eagle Rock area of Los Angeles.

Backes stressed there was no need to buy pot from Mexican cartels because more than enough quality marijuana is legally grown in California to supply the dispensaries.

Drug Enforcement Administration spokeswoman Casey McEnry, who works in the San Francisco office, said it was difficult to substantiate or refute Baca's claims because of challenges in determining where pot found in dispensaries was produced.

Baca, however, said chemical analyses of pot confiscated during drug raids against street dealers showed similar pesticide content and other characteristics as marijuana sold in dispensaries.

Allegations of criminal activity involving pot shops increased after a string of deaths, including the Aug. 26 slaying of three men in West Hollywood who police suspect had been buying up bulk quantities of high-grade marijuana from dispensaries and reselling it on the street.

A suspect in that case confessed to killing the men when he didn't have enough cash to complete a transaction, police said.

In addition, two workers at different dispensaries have been killed during robberies in recent weeks.

"It is no surprise that people are going to get killed ... drugs and violence go together," Baca said.

The ballot measure that would legalize marijuana is Proposition 19. Los Angeles police Chief Charlie Beck said his department had not taken a position on the measure, but he was personally opposed to it.

"We already have enough ... substances that cause issues with people's lives," Beck said. "We already have enough misery."

Despite his concerns about the way dispensaries operate, Baca has been a longtime advocate of medical marijuana use by AIDS patients and people with other chronic conditions.

The 1996 law approved by California voters allows collectives to grow medicinal marijuana, though they are not supposed to make profits and can only charge enough to cover operating expenses.

Baca said the intent of the law was good but had been corrupted almost beyond recognition with most "patients" producing spurious notes from doctors describing vague ailments that don't need to be treated with marijuana.

"People (are) going into these dispensaries with silly notes from the doctors saying they have a headache or a sore toe," Baca said.

Thirteen other states have legalized medical marijuana, and many jurisdictions around the country have decriminalized marijuana to the point that low-level possession offenses aren't prosecuted.

Craig Reinarman, professor of sociology and legal studies at the University of California, Santa Cruz, said law enforcement officials usually oppose drug legalization efforts because they are interested in maintaining the status quo and holding onto federal drug-fighting money associated with it.

"They have to use rhetorical strategies of invoking the frightening specter of Mexican drug cartels," Reinarman said. "I don't see any reason to see this as anything other than a completely self-interested claim that can't be substantiated."